At this moment, there aren't any way to privately share clonables to other Webflow users without manually send them to their accounts, alternatively sharing them on the showcase (which defeats the purpose of a "private" clone).
I would like to see a way to share clones privately through a simple link, which another user clicks on and clones the component or project.
This would be great for building private, sellable third party component libraries, templates, easily share clones with other team members etc. without having to spend the time of manually send over the clones to other members.